Various valves for fluid control are in wide use in industry. One type of such valve is known as a knife gate valve. In a knife gate valve, a relatively flat knife gate, also referred to as a blade, is translatable back and forth with respect to an aperture in a valve body to open or close a fluid flow passage in the valve body.
Many such knife gate valves are best adapted only for dealing with pressure in a single direction. That is, in such a single direction valve, when the valve is closed the high pressure side will tend to urge or force the blade in the direction towards the low pressure side so that the blade is forced into a seating arrangement against a valve seat that is part of the body. In such a one-directional arrangement, the seating is accomplished by the low-pressure face of the blade being urged into tight contact with the body the low-pressure side of the seat. These single direction knife gate valves are relatively economical and easily to manufacture, because the pressure of the fluid itself helps assist with seating.
A disadvantage with these single direction knife gate valves, however, is that they often are not suitable for use as dual direction valves. Typically, if pressures are reversed from the intended orientation, the blade might be urged away from its seat, and positive closure may not be obtained.
One approach for overcoming this problem has been to form a valve with two seats, one on each side of the blade. However, this can be relatively expensive.
Another approach to creating bi-directional sealing has been the use of a perimeter seal around the perimeter edge of the blade. However, in some applications the perimeter seal also has disadvantages, as far as exposure, complexity and/or durability.
Accordingly, it would be desirable to have an improved knife gate valve assembly and method that can accomplish dual directional flow shutoff when desired. It would also be desirable for such a dual directional knife gate valve assembly and method to be convenient and easy to manufacture, assemble, and maintain.